The present invention relates to the reinforcement of high-tension-resistant steel for prestressed concrete members or buildings.
In the production of prestressed concrete and also with prestressed concrete buildings or members, as, for example, in prestressed concrete pressure containers, the reinforcemens are wound under tension onto the outside of the container wall and later, to prevent corrosion, are enveloped with a corrosion inhibitor or compact material, e.g., cement mortar.
The adherence of the reinforcements is of considerable importance. This applies especially to reinforcements which are embedded without end anchoring in the cement mortar. It is also applicable to reinforcements which are located through intermediate anchoring, e.g., on a container wall or at the rear wall by winding channels placed in a container wall. These horizontal windings channels of rectangular cross section are at first open toward the outside, but later are pressed out, e.g., after a one-time or repeated retensioning (restressing) of the reinforcements with the corrosion inhibitor or compact material. Such reinforcements, depending on the internal pressure prevailing in the pressure container or depending on the circumferential stress occurring in the container wall, the counteracting circumferential stresses to be generated by the reinforcements in the container wall, are wound in several layers running radically on top of one another and in helical windings adjacent to one another.
The tight enveloping of each reinforcement winding and layer by the corrosion inhibitor or compact material is of great significance. This applies especially when using a compact material e.g., cement mortar, or a tightly closed compact cross section is to be formed. It is also important in view of possible reinforcement breakage and its consequences. The more perfectly the reinforcement windings and layers are embedded in the cement mortar, the smaller is the likelihood that during a reinforcement break an entire reinforcement layer, if only between two intermediate anchorings, unravels. For such perfect embedding of the reinforcements it is necessary that the reinforcements, both within each layer between their windings, and also from layer to layer are sufficiently spaced apart so that the cement mortar to be introduced later, can seep through to all interstices. However, such spacings within a reinforcement bundle or within a reinforcement layer must also be present if the reinforcements and/or their windings are to be enveloped by a protective material, e.g., rust-proofing grease, instead of by a compact material. Otherwise, during the subsequent introduction of such material, there is no guaranty of a perfect rust-proof envelopment of the reinforcements by the material.
It is already known in the art how to increase the adherence of the reinforcements by their profiling. It is also already known to have reinforcements of round or oval cross section made from rod-or ribbon-like reinforcement steel in the manner of twisted concrete cross section steel. Known, furthermore, is the so-called rack tool steel which is provided with a large number of small small beads to increase the adherencce effect. It is, moreover, known to use instead of homogeneous round or oval steels for the formation of multilayer outside windings on container walls or in winding channels of the kind stated above, stranded cables of high-tension-resistant steel wires which can be produced with a relatively large cross section and can be bent with a small radius of curvature. For example, seven-strand cables with an outside diameter of 10 to 15 mm and cross sections of about 140mm.sup.2 or larger, are particularly well-suited for reinforcement windings of the type described. They have good relaxation and stress-removal properties for manufacture. Also, such stranded cables, in contrast with homogenous round or oval steel of similar cross-section sizes, can be manufactured in very long lengths, so that much fewer reinforcement joints than with homogeneous steel are required. However, in the case of reinforcements with a large number of stranded cables or stranded cable windings, the grooves between the tightly packed strands or their windings do not provide sufficient space to make possible complete penetration of a reinforcement bundle or packet and a perfect enveloping of the individual reinforcements and/or their windings. Even with the known ribbed or beaded rack tool steel and stranded cables, where the outside wires are profilated, i.e. provided with ribs, this possibility does not exist. These ribs are to provide better adherence to the concrete and a more simple anchoring. Since for stranded cables, without exception, colddrawn wires of high strength are used, only very low ribs can be produced if the strength of the steel is not diminished. The rib heights are around 0.15 mm.
Therefore, it has been proposed that spacers be inserted into a winding or tensioning channel. These spacers separate both individual stranded cables or reinforcements of rod- or ribbon-like reinforcement steel, and individual windings and/or layers of such reinforcements. During the subsequent pressing out of the winding or reinforcement channel, these spacers make possible the free flow of the protective material e.g., of cement mortar. However, the installation of such spacers requires extra effort and restricts the use of machines for bundling the reinforcements.
It is, therefore, an object of the invention to provide a reinforcement comprising either a homogeneous reinforcement steel or a multistranded cable in such a way that both its adherence to a protective or compact material is improved, and assurance is provided that during winding around a concrete member or building, e.g., a container wall, there is formed inside or outside the winding channel a mutual space between the reinforcement windings and the reinforcement layers; this space must be large enough to assure complete envelopment of the reinforcement by the protective or compact material.
Another object of the present invention is to provide a reinforcement of the foregoing character which is simple in design and may be economically fabricated.
A further object of the present invention is to provide a reinforcement arrangement as described, which has a long service life.